Can nuclear strategy and morality be compatible? The Roman Catholic bishops of the United States have just addressed this question in their draft pastoral letter. Three important moral dilemmas are raised.

First, can initiating the use of nuclear weapons ever be morally justified? The dilemma arises because it is not known whether, in a conventional war, the use of nuclear weapons in an extremely limited fashion - to destroy a Soviet radar site, for example - would be more likely to lead to nuclear escalation or to stop the conventional war. If initiating the use of nuclear weapons led to escalation, the action would have been immoral. But if it led to a quick end of the conventional war in Europe, might not the action be seen as moral? Perhaps. But every effort would have to be made to keep close control of the risks: Small weapons would be needed; there should be no delegation of authority to dispersed military units; continual communications with the Soviet Union must be maintained; and there should be a clear idea of how to terminate the conflict.

Even then, such an action could only be a last resort. What morality and prudence dictate is a ''no early use'' of nuclear weapons policy, and highly selective and limited use if it should come to that. Indeed, morality and prudence suggest that, were deterrence to fail, one should have the means to carry out an alternative, no-nuclear strategy.

The second dilemma that the bishops have raised is whether it is right to have nuclear forces and a targeting doctrine that deliberately aim at civilians. The bishops believe not. Many others differ over this issue. Some have argued that assured destruction is an immoral doctrine because it rests on the deterrent threat of disproportionate damage to civilians and industry. The American government does not aim its weapons at the Soviet population per se, and ever since the 1950s US doctrine has in practice involved military targets. But many people also powerfully argue that counter-force targeting is immoral because it makes nuclear weapons seem more usable, and requires ever more war-fighting capabilities. Moreover, destruction of large parts of civilian society is an unavoidable part of any large-scale strategic nuclear war.

Targeting certainly raises an important moral issue. But the theology of ''counter-force vs. counter-city,'' while not irrelevant, is less important than whether our strategy and arsenal can reduce the prospect of war in a time of crisis. The truly immoral behavior is to have nuclear forces and doctrines that invite preemptive attack. For example, a force that is highly lethal and highly vulnerable at the same time will tempt a political leader to ''use it or lose it'' at a time of crisis. The crucial moral question about force posture and targeting doctrine therefore is: How can our current actions ensure that even in a deep crisis no general on either side can persuasively argue that it is imperative to launch his nation's strategic forces because they might otherwise be destroyed?

A third dilemma raised by the bishops' letter concerns the morality of deterrence itself. Is it justifiable to threaten a nuclear attack that might destroy innocent civilians if the intention is to deter nuclear war altogether? Even if the consequences of the threat are moral - if deterrence works, in other words - is making the threat itself morally acceptable? Some theologians believe it is not. They argue that it is wrong to threaten what it is wrong to do. And yet to remove the threat altogether - on the grounds that it is evil to threaten to attack military targets with weapons that might be neither discriminating nor controllable - could itself have disastrous moral effects. It could incite adversaries to take greater risks, and thereby make nuclear war more likely.

Although we may differ with the bishops on the specifics of nuclear strategy, we agree with their general conclusion that nuclear deterrence is only conditionally moral; the condition being that we make genuine efforts to reduce dependence on nuclear deterrence over the long run. To resort to nuclear deterrence to protect low stakes is a morally and politically nasty bluff. To resort to nuclear deterrence to protect high stakes makes political and moral sense only if the credibility of the threat is enhanced by the availability of nonnuclear weapons, which may make the actual execution of the threat unnecessary.

A complacency that led one to relax about the dangers of relying on nuclear deterrence could become the source of great immorality. But so also would a utopianism which could raise both nuclear and conventional risks.

In short, nuclear deterrence can be tolerated, but never liked. Deterrence can be seen as a necessary evil. Because it is necessary one cannot abandon it carelessly; because it is evil, one must strive to rely on it less.